The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to perform etching and/or other treatment of substrates such as semiconductor wafers. A substrate may be arranged on a pedestal in a processing chamber of the substrate processing system. For example, during etching in a plasma etcher, a gas mixture including one or more precursors is introduced into the processing chamber and plasma is struck to etch the substrate.
The pedestal in the processing chamber may comprise an electrostatic chuck (ESC) to hold substrates in place during etching. The ESC can require heating apparatus and other circuitry mounted in the pedestal to control operation of the ESC. The circuitry may be provided in a printed circuit board assembly (PCBA). A PCBA can be relatively complex, with as many as 250 to 300 components on a single printed circuit board in the PCBA. Those components could include, for example, a field programmable gate array (FPGA), a central processing unit (CPU), and/or various kinds of measurement circuitry, such as a voltage divider circuit. A PCBA also may include multiple layers, each with circuitry mounted thereon. Some of the layers may be primarily grounding layers; others may be power layers; others still may be signaling layers, providing various types of signaling to control operation of the ESC.
Conditions within a substrate processing chamber can vary widely, depending on the process being implemented, and on conditions that can exist between processing operations. The varying conditions include temperature, which can vary outside of operational temperature ranges of circuitry in a PCBA. Those temperature conditions can exist for a sufficiently long time that PCBA circuitry can fail, or otherwise cease to operate. In addition, temperature can continuously cycle over a very wide range, for example from −40° C. to +70° C., in a short time, for example within four minutes, over a long period of time, even a number of days. The cycling is expected throughout the life of the PCBA. The cycling range could be even wider, as colder temperatures (even −60° C. or −80° C. or −140° C.) come into play.
Moreover, large temperature variations impose significant expansion or contraction of materials in the PCBA. Different materials in the PCBA will have different coefficients of thermal expansion, perhaps significantly different. As a result, these materials, which may be soldered or otherwise attached to each other, can expand or contract to different extents, thereby imposing a strain on the solder or other attachments, and causing fatigue. Such fatigue can cause soldered connections to break or otherwise come loose, resulting in PCBA failure, and consequent downtime of the substrate processing chamber.
To avoid effects such as solder joint fatigue, it is desirable to keep PCBAs relatively constant in temperature. But heating a PCBA, for example, could also entail undesired heating of surrounding portions of the substrate processing chamber.
A PCBA may contain measurement circuitry, such as voltage or current measurement circuitry, whose performance can fluctuate widely as a function of temperature. The measurements themselves can vary widely as a function of temperature. If temperature fluctuations of the measurement circuitry on the PCBA are not constrained, it may not be clear whether fluctuating measurements are the result of the fluctuating values themselves, or the changing performance of the measurement circuitry, or a combination of the two.
In view of the foregoing, it would be desirable to provide a mechanism to heat a PCBA locally, without affecting conditions elsewhere in a substrate processing chamber. It also would be desirable to provide a mechanism to promote maintenance of temperature of the PCBA, or of certain components, within a predetermined range.